Generally, a hot-start situation is meant when, for example, after a short operating pause, a renewed start takes place in an internal combustion engine which is still hot. In a hot engine at rest, fuel vapor bubbles form in the fuel line as well as in the injection valve itself. In the next start operation, these fuel vapor bubbles then hinder the regular metering of fuel.
For this reason, an extended injection signal is, for example, outputted under hot-start conditions so that a certain minimum quantity of fuel can be made available for the injection process even when there is an occurrence of the fuel vapor bubbles.
German patent publication 4,039,598 discloses a hot-start method and a hot-start arrangement for an internal combustion engine. A hot-start situation is then assumed in accordance with the teaching presented there when the engine temperature as well as the intake air temperature exceed specific threshold values and, furthermore, the difference in magnitude between the intake-air temperature at an earlier time point and the intake-air temperature at a new start lies above a selectable threshold.
German patent publication 4,435,419 discloses a control system for metering fuel to an internal combustion engine. Here, a hot-start situation is assumed and a corresponding hot-start bit is set when the engine temperature exceeds a first threshold value and, in addition, an increase of the intake air temperature by a specific amount has taken place since the last measurement. The last value can be that value which was present at the time point of switching off the engine and the new value can be obtained at the time point of switching on the ignition or the starter. The hot-start bit remains set until the engine temperature has dropped below a second threshold value or until a predetermined total air mass has flown through the intake manifold. The last-mentioned total air mass is determined by means of an integration of the signal of an air-mass sensor in the intake manifold.
A method and an arrangement for controlling the metering of fuel in an internal combustion engine are known from German patent publication 195 47 644. Here, the fuel quantity, which is to be injected, is corrected in dependence upon the temperature, the density and the pressure of the fuel. The method of German patent publication 195 47 644 is preferably utilized in self-igniting internal combustion engines which are equipped with a common rail system.
Especially in modern fuel injection systems (which systems operate with a high-pressure fuel injection), some components become hot such as the high-pressure pump even after switching off the engine whereby increased temperature values can occur compared to the switch-off temperature. For a subsequent hot-start situation, the correct metering of fuel is of special significance so that a certain and reliable start is ensured. An essential aspect is also the hot-start recognition itself.